Screening of Multitarget-Directed Natural Compounds as Drug Candidates for Alzheimer's Disease Using In Silico Techniques: Their Extraction and In Vitro Validation

Alzheimer's disease (AD) is a neurodegenerative disorder that impairs neurocognitive function. Acetylcholinesterase (AChE) and beta-site APP cleaving enzyme 1 (BACE1) are the two main proteins implicated in AD. Indeed, the major available commercial drugs (donepezil, rivastigmine, and galantamine) against Alzheimer's are AChE inhibitors. However, none of these drugs are known to reverse or reduce the pathophysiological condition of the disease since there are multiple contributing factors to AD. Therefore, there is a need to develop a multitarget-directed ligand approach for its treatment. In the present study, plant bioactive compounds were screened for their AChE and BACE1 inhibition potential by conducting molecular docking studies. Considering their docking score and pharmacokinetic properties, limonin, peimisine, serratanine B, and withanolide A were selected as the lead compounds. Molecular dynamics simulations of these protein-ligand complexes confirmed the conformational and energetically stabilized enzyme-inhibitor complexes. The inhibition potential of the lead compounds was validated by in vitro enzyme assay. Withanolide A inhibited AChE (IC(50 )value of 107 mu M) and showed mixed-type inhibition. At this concentration, it inhibited BACE1 activity by 57.10% and was stated as most effective. Both the compounds, as well as their crude extracts, were found to have no cytotoxic effect on the SH-SY5Y cell line.